1. Field of the Invention
The present invention relates to an oxide phosphor for use in an electroluminescent device and to an electroluminescent device containing the phosphor.
2. Background Art
Conventionally, sulfides, particularly zinc sulfate (ZnS), have frequently been employed as phosphors for use in an electroluminescent device (hereinafter referred to as EL device). In recent years, as a new phosphor thin film for use in EL devices, there has been developed oxide phosphor thin film which contains gallium (Ga) and/or calcium (Ca) and to which an arbitrary luminescence center has been added (Japanese Patent Application Laid-Open (kokai) No. 10-270168).
However, in red, green, and blue emissions, which are required when full-color emission is to be realized, the aforementioned sulfide phosphors cannot attain sufficient calorimetric purity or luminance that would allow them to be put into practice. In addition, they are chemically unstable, and particularly very unstable when exposed to moisture. Thus, a special sealing treatment of thin film EL devices must be carried out in order to completely remove moisture, posing a crucial problem; i.e., elevating production costs of the devices.
Oxide phosphor thin films employing oxide phosphors such as Mn-doped zinc silicate (Zn2SiO4:Mn) have already been put into practice as chemically stable phosphor material for use in EL devices (as disclosed, for example, in Japanese Patent Application Laid-Open (kokai) Nos. 04-209693 and 10-270168). Most of the above oxide phosphors comprise, as host material, ternary compounds or multi-component oxides, and their complex compositions make these compounds and oxides difficult to form into thin film of excellent crystallinity. In order to attain high luminance, the phosphors must undergo heat treatment at a comparatively high temperature. Thus, disadvantageously, phosphor thin film of a desired composition cannot be produced with high reproducibility.
In view of the foregoing, the present inventors have carried out extensive studies in order to solve the aforementioned problems and have found the following: Although Y2O3:Eu, which is known to serve as a cathodolumin (CL) luminescence phosphor or a photoluminescence (PL) phosphor, is unusable as an electroluminescence (EL) phosphor, when manganese is added to its matrix Y2O3xe2x80x94a binary compound which is readily crystallizedxe2x80x94the resultant Y2O3:Mn, which cannot act as a CL or PL phosphor, acts as an excellent electroluminescence (EL) phosphor. The present invention has been accomplished on the basis of this finding.
Thus, an object of the present invention is to provide an oxide phosphor for use in an electroluminescent device, which phosphor is capable of providing a high-luminance EL device while the composition thereof is controlled to be as simple as possible, and which phosphor attains multi-color and full-color light emissions without need for treatment at a high temperature greatly in excess of 1,000xc2x0 C. Another object of the invention is to provide an electroluminescent device employing the phosphor.
Accordingly, in a first aspect of the invention, there is provided an oxide phosphor for use in an electroluminescent device, which phosphor comprises an yttrium (Y) oxide as a matrix and at least one transition metal element as an activator.
Preferably, the yttrium oxide is yttrium oxide (Y2O3).
Preferably, the phosphor further contains at least one rare earth metal element as the activator.
Preferably, the phosphor contains the transition metal element in an amount of about 0.1-10 at. % based on yttrium (Y).
In a second aspect of the invention, there is provided an oxide phosphor for use in an electroluminescent device, which phosphor comprises, as a matrix, a Yxe2x80x94Gexe2x80x94O oxide containing yttrium (Y) and germanium (Ge) and, as an activator, at least one metallic element.
Preferably, the phosphor contains germanium (Ge) in an amount of about 0.01-99 mol % based on the total amount of the Yxe2x80x94Gexe2x80x94O oxide containing yttrium (Y) and germanium (Ge).
Preferably, the matrix is a complex oxide comprising yttrium oxide (Y2O3) and germanium oxide (GeO2).
Preferably, the matrix is at least one ternary compound selected from the group consisting of Y2GeO5, Y2Ge2O7, and Y4GeO8 (yttrium germanates).
Preferably, silicon (Si) is partially substituted for germanium (Ge) in the matrix.
Preferably, the Yxe2x80x94Gexe2x80x94Sixe2x80x94O phosphor contains silicon (Si) in an amount of about 0.01-99 mol % based on the total amount of an oxide of germanium (Ge) and silicon (Si).
Preferably, the activator is at least one metallic element selected from the group consisting of transition metal elements and rare earth metal elements.
Preferably, the phosphor contains the metallic element in an amount of about 0.1-10 at. % based on yttrium (Y).
In a third aspect of the invention, there is provided an electroluminescent device employing, as a light-emitting layer, an oxide phosphor for use in an electroluminescent device as recited above.
Preferably, the light-emitting layer is a thin film.